Generally, embodiments of the present invention relate to structures and methods of manufacturing utilizing direction of force loading or shock induced deformation of structures including microstructures produced in accordance with embodiments of the invention. Examples include a distributed longitudinal loaded plate apparatus and method of manufacturing. Embodiment of the invention can produce desired structural performance under such force loading such as strain loading. Embodiments of the invention also relate to distributing load of an impact over a greater surface area without having to change mass or materials associated with a design. Alternatively, an embodiment of the invention can be used to use variants of the invention to achieve improvements in size, mass or other physical characteristics.
Material properties of a structure or material can change with a material's grain: size/shape/orientation relative to a force load. The term grain can refer to crystallites which can include a description of different degrees of organization such as crystalline, polycrystalline, or amorphous structural organizations. Grain boundaries can be described as interfaces where crystals of different orientations meet. A grain boundary is a single-phase interface, with crystals on each side of the boundary being identical except in orientation. Grain boundary areas contain atoms that have been perturbed from their original lattice sites, dislocations, and impurities that have migrated to the lower energy grain boundary. Grain boundaries disrupt the motion of dislocations through a material. Dislocation propagation is impeded because of the stress field of the grain boundary defect region and the lack of slip planes and slip directions and overall alignment across the boundaries. Polycrystalline materials are solids that are composed of many crystallites of varying size and orientation. Grains are small or even microscopic crystals and form during the cooling of many materials. Their orientation can be random with no preferred direction, that can be described as having a random texture or direction, possibly due to growth and processing conditions. Areas where crystallite grains meet are known as grain boundaries. Most inorganic solids are polycrystalline including all common metals and many ceramics.
Research in this inventive effort discovered, among other things, that the nature of materials or structures under investigation can show behavior that can change under certain types of force loading or high strain rates (shocks, etc) on structures design according to embodiments of the invention. Materials that resist motion (failure) under lower strain rates can reverse normal behavior and promote motion under high strain due to behavior of dislocations in a material(s). A dislocation can be a crystallographic defect, or irregularity, within a crystal structure. A presence of dislocations can strongly influence many properties of materials. For example, dislocations can stop motion and make materials stronger/brittle. Dislocations are in the way of movement. However, high densities of organized dislocations can become slip paths for exemplary material subjected to an exemplary force such as shocked material. What was strong becomes ductile. Efforts were made to develop ways of utilizing direction of shock induced deformation including in design of shape charges as well as other structures.
A problem encountered with regard to development of some embodiments of the invention arose in association with analysis of munitions that found a variation in the depth of penetration of a shaped charge jet sufficiently critical to alter application of such munitions. A shaped charge 1 can be an explosive charge 3 designed to focus the energy of the explosion to perform more work than could otherwise be done with bulk explosives alone. A shaped charge 1 can be a cylindrical charge 3 with a detonator 5 at one end and a hollow cavity 7 at the other. The cavity 7 can serve to focus gaseous detonation products resulting in an intense localized energy or force referred herein as a “jet”. The shaped charge cavity 7 can be lined with thin metal but other materials such as glass or ceramics can also be used (e.g, sometimes referred to as a liner). Shaped charges 1 can be constructed in many different designs, shapes and sizes. One configuration can be a charge 3 and a thin, conical copper liner 7 with an apex angle 9 less than 60°. A distance between the shaped charge 1 section with the cavity 7 oriented towards a target 8 can be referred to as a stand-off distance 10. Effectiveness of a shaped charge can be related to characteristics of the jet. The jet works by pushing target 8 material out of its way and forming, e.g., an entry hole in the target 8. Little of the target's 8 material is consumed or ejected from the entry hole. Instead, target material is compressed into the side of the hole. Operation of a shaped charge is a violent, explosive event. The explosive generated shock front interacts with the liner. Under extreme temperature and pressure the liner material takes on the properties of an inviscid, incompressible fluid but remains a solid material undergoing extreme deformation best described with visco-plastic relationships. The explosive energy associated with the charge in this study accelerates the liner material to velocities beyond 13 mm/μs (13,000 m/s) and at extreme pressures over 25 GPa. An exemplary strain rate ({acute over (ε)}) exceeds 5×106 s−1. During this process, the direction in which the slip planes in the material form change to comply with the overwhelming forces driving liner collapse. The collapse of the liner is described as a series of concentric cones flowing into a series of concentric cylinders. The length is defined by the ability of the material to stretch and remain coherent.
Strain with respect to the jet can be associated with a differential in the velocity of the tip and tail. The greater the difference in these velocities, the greater the rate of elongation will be and the greater the jet length at a given distance or time of flight. The maximum length of a shaped charge jet can be determined from the added total length of the individual particles after jet breakup. Jet length is of primary importance in determining shaped charge performance. In some contexts, assuming a constant density of target and jet, target penetration can be a direct function of jet length.
Shaped charge performance can be defined by penetration depth. Penetration depth increases with jet length, and jet length is maximized by materials that are able to undergo significant strain without failure. Because the jet stretches as it proceeds towards the target, there can be a relationship between performance (defined by Lj) and the time (t) of flight and the associated distance (D), or “standoff”, between the charge and the target. For all shaped charges, there is a distance at which the jet can no longer remain coherent. This can be a point of optimal performance. A slug can be a more massive section of material traveling at a lower velocity following the jet. The slug is capable of widening the impact hole but is not generally associated with penetration depth. The ratio of jet to slug is a function of shaped charge design.
Some materials exhibit extreme ductility under the intense dynamic conditions involved in the shaped charge collapse process. Within a common material or alloy, factors such as material texture, grain size and shape are known to affect jet elongation. Finer grain size can be attributed to jet elongation.
Reduced grain size can improve jet elongation and charge performance. Grain size is associated throughout liner material characterization in various forms of the Hall-Petch relationship which includes yield stress. Yield stress (σy) is related to a basic yield stress (σyo) that can be regarded as the stress opposing the motion of dislocations, k (Petch slope) is a constant indicating the extent to which dislocations are piled up at barriers (grain boundaries, inclusions, etc) and d is a grain diameter. Other forms of Hall-Petch reflect flow stress, residual stress, lattice frictional stress, and hardness to a factor of, e.g., grain size-½. Hall-Petch relationships are valid below a recrystallization temperature of a material of interest.
Crystallographic texture describes the distribution of crystallographic orientations of the microstructure. A degree of texture describes the percentage of crystals having a preferred orientation. A value of relative concentration (R) with respect to a distribution expected in a sample with random grain orientation. Orientation distribution function (ODF) is another measure of texture defined as a volume fraction of grains oriented along a direction.
Shear bands are another described characteristic of shaped charge kinetics. These bands are characterized by massive collective dislocation activity in a narrow deformation zone with the adjacent matrix described by comparably low and homogeneous plastic flow. Shear band formation is promoted when homogeneous dislocation slip is inhibited or when an insufficient number of slip systems is available (weak and/or unfavorable texture). Shear banding is also associated with sudden drops in local flow stress and can be considered as a softening mechanism. They are also characterized as dislocation highways and dominant paths.
Relationships exist between microstructure and shaped charge performance. Liner deformation starts as the material interacts with the shock front. As a shock passes through material it generates dislocations, strain hardening and microstructural defects. Some primary deformation mechanisms associated with shock loading are dislocation generation and motion. The substructure generated depends on a number of shock wave and material parameters. The dislocation density (ρ) is directly related to pressure. A width of the shock wave is a function of grain size, pressure and time.
In one particular example, a short standoff associated with an application of such a munition suggested that jet formation and early velocity were of concern, not ultimate jet elongation. While manufacturing history suggested a metallurgical investigation, resolving the effect of undesirable variation in performance of a particular munition, e.g., shaped charge, required a systematic approach to investigate all potential causes. A variety of hypotheses were formulated and investigations resulted.
Eventually efforts included a metallurgical study and a focus of research turned to an investigation into if and how variables in cold working affect materials such as 1100 aluminum metallurgical properties and shaped charge performance. Shaped charge performance typically can be a function of jet length. Jet length is the stretch of elongated, coherent liner material flowing from a detonation of a shaped charge. Jet length is typically described as a distance of elongation at either the time of target impact or the moment of jet break up as it travels through open air. Shaped charge jet elongation is a function of the ability of the material to yield and demonstrate stable flow under very high strain rate. Jet elongation is associated with a differential between the velocity of the tip or front of the jet and that of the tail or rear of the jet. In this application, early formation and maximized elongation over short distances are important because standoff distance is short.
Research and conception efforts in one embodiment of the invention, shaped charges, lead to formation of a hypothesis that a given manufacturing process generates a characteristic microstructure in the material, and the response of a given liner to the explosive loading is a function of the inherent microstructure of the liner. This affects the deformation of the liner and initial jet formation under an explosive force load applied to the liner experienced during shaped charge collapse. Effects on deformation resulted in changes in an ability of a material to flow and efficiently form the shaped charge jet. Deformation under dynamic loading conditions is controlled by the microstructural features such as grain size, grain shape, orientation (both crystallographic and physical), size, shape, amount, location and distribution of inclusions. Inherent strengths and alignment of these microstructural features with respect to shock loading direction and shaped charge kinetics determine the flow of the liner material during liner deformation.
Aspects of this research effort focused on early jet formation thus it became necessary to observe representative shock-deformed material. Thus, a variety of new approaches to conducting such observations were necessarily created given a lack of existing capability to do so. Reliance upon existing capture experiments or equipment would not been capable of making needed observation thus would have only provided recovered material that witnessed the full deformation event thus masking or obliterating early deformation. This need for new experimental capabilities to conduct this inventive effort resulted in successful design, execution and validation of a unique experimental techniques allowing for a practical recovery of shocked shaped charge liners arrested in the first few microseconds of flow. The new experimental capability required only a small percentage of the explosive mass of the full charge, yet allowed experimentation with full-scale, as-fabricated (i.e. actual) liners. Recovery only involved about 100 gallons of water and a dip net. Material recovered from this experiment provided an opportunity for direct observations needed to conduct necessary research and discovery such as formation of the axial hole that often occurs in the center of a shaped charge jet; marked differences in the ability of material to flow associated with change in temper; formation of shear bands and strain during shaped charge collapse; development of texture during early shaped charge liner flow; anisotropy in the microstructure introducing the possibility of further refinements; and tensile fracture around the base of the liner. From examination of the effects of microstructure on early collapsed formation, new correlations between material properties and shaped charge collapse kinetic equations were derived. The process of developing these equations involved critiquing a set of hypotheses concerning the material science supporting shaped charge collapse. Ideally, these relationships will assist other research in this field and support further optimization of force loaded structures with similar desired structural properties such as charge design or with high-strain deformation applications in general.
This research gave rise to development of new designs such as an asymmetric scaled shaped charge design. The focus on early jet development initiated related discussions that evolved into a shape design capable of holding target hole diameter constant while varying penetration depth and charge explosive weight. Traditionally, all of these variables scale together. Benefits of these efforts and discoveries include providing an ability to create resulting designs projected to have approximately 60% of their original performance for 30% of an original explosive mass.
According to an illustrative embodiment of the present disclosure, a method of manufacturing and structure is provided including a process for exploiting relationships between a structure subjected to a force loading, e.g., a shaped charge liner, manufacturing processes, microstructures of the structure with respect to orientation of the force loading and design of the structure, and resulting desired behavior of the structure in response to the force loading, e.g., shaped charge jet formation.
For example, an exemplary embodiment can include providing a metallic plate; forming said plate such that an original longitudinal direction of rolling the plate is perpendicular to a long direction of the plate, thus an applied force loading on the plate in its end application structure would then be distributed over the longitudinal direction. Large and small grain microstructures can be manipulated or created with respect to manufacturing processes and direction of force loading with respect to the microstructure orientation(s) to create different structural or material properties. Embodiments of the invention provide a design process to create microstructural features of an end application structure based on the microstructural response to force loading such as high strain rates (e.g., during shaped charge jet formation after application of the shaped charge explosive force). Embodiments of the invention include a focus on a role of microstructure in controlling or influencing deformation mechanisms and material properties during application of force loading on a structure designed and produced according to an embodiment of the invention e.g., a shaped charge collapse and early jet formation.
Additional features and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following detailed description of the illustrative embodiment exemplifying the best mode of carrying out the invention as presently perceived.